1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device which processes a substrate including a semiconductor substrate, and more particularly to such a method including a step of forming a coating oxide film in a recess of the substrate.
2. Description of the Related Art
Semiconductor devices such as NAND flush memories necessitate microfabrication. An element isolation region is formed by a shallow trench isolation (STI) process in these semiconductor devices. In the STI process, a silicon oxide film or the like is buried in a trench formed in an upper surface of a semiconductor substrate so that an element isolation region is formed. A high density plasma (HDP) film has conventionally been buried in a trench by a plasma chemical vapor deposition (PCVD) process. However, with progress of microfabrication in design patterns, it has become more and more difficult to sufficiently fill a trench.
In view of the circumstances, the use of a coating oxide film such as spin on glass (SOG) has recently been proposed. The coating oxide film includes a polysilazane (PSZ) film, for example. When a coating oxide film is to be formed on a semiconductor substrate, a coating liquid is applied to the semiconductor substrate. Consequently, the coating liquid can reliably fill an interior of a trench which is located in a region with a high aspect ratio such as a memory cell region and has a small opening width. Furthermore, the coating liquid can also be buried thick in a larger region such as a peripheral circuit region in the trench interior.
Subsequently, a thermal treatment needs to be applied to the coating oxide film applied to the semiconductor substrate in the aforesaid manner so that the coating oxide film is hardened. Furthermore, impurities such as carbon (C), nitrogen (N) and the like need to be removed from the coating oxide film. In the case of the polysilazane film, however, the aforementioned thermal treatment causes film contraction which results in high stress fluctuations. As a result, a crack occurring in the coating oxide film sometimes reaches the semiconductor substrate.
In order that occurrence of cracks may be prevented, for example, Japanese published patent application JP-A-2007-27697 discloses a method in which a combination of a thermal treatment with several treatment steps and an aqueous cleaning with several treatment steps is carried out during a stabilization treatment by thermal treatment. However, the aforesaid combined treatment increases the number of treatment steps, thereby increasing the manufacturing cost. For example, a low-temperature water vapor generation (WVG) oxidation (oxidation by hydrogen combustion) is carried out after the coating of a PSZ film. Thereafter, several steps of a treatment by heated water or a sulfuric acid peroxide mixture (SPM) treatment are sometimes added for the purpose of stabilization of the PSZ film. Furthermore, there is a case in which are required a second step thermal treatment and subsequent several steps of the treatment by heated water or SPM treatment.